Network Working Group B. Leiba
Internet-Draft Huawei Technologies
Updates: 3501,6154 (if approved) E. Iceman
Intended status: Standards Track Google, Inc.
Expires: October 15, 2013 April 15, 2013
IMAP $Important Keyword and \Important Special-Use Attributedraft-iceman-imap-specialuse-important-02
Abstract
RFC 6154 created an IMAP Special-Use LIST extension and defined an
initial set of attributes. This document defines a new attribute,
"\Important", and establishes a new IANA registry for IMAP folder
attributes, registering the attributes defined in RFCs 3348, 3501,
and 6154. This document also defines a new IMAP keyword,
"$Important", and registers it in the registry defined in RFC 5788.
Status of this Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2Leiba & Iceman Expires October 15, 2013 [Page 1]

Internet-Draft IMAP "Important" Keyword and Attribute April 2013
1. "$Important" carries a specific meaning of importance, as opposed
to urgency. It is meant to be used for a form of triage, with
"\Flagged" remaining as a designation of special attention or
particular urgency.
2. The setting of "$Important" is expected to be based at least
partly on heuristics, whereas "\Flagged" is intended to be set by
the user.
3. Definition of the 'Important' Mailbox Attribute
The "\Important" mailbox attribute is a signal that the mailbox
contains messages that are likely important to the user. In an
implementation that also supports the "$Important" keyword, this
special use is likely to represent a virtual mailbox collecting
messages (from other mailboxes) that are marked with the "$Important"
keyword. In other implementations, the system might automatically
put messages there based on the same sorts of heuristics that are
noted for the "$Important" keyword (see Section 2). The distinction
between "\Important" and "\Flagged" for mailboxes is similar to those
between "$Important" and "\Flagged" for messages.
3.1. Formal Syntax
The following syntax specification adds to the one in [RFC6154],
Section 6, using Augmented Backus-Naur Form (ABNF) as described in
[RFC5234].
use-attr =/ "\Important"
3.2. Example
In the following example, the mailbox called "Important Messages" is
the one designated with the "\Important" attribute.
C: t1 list "" "Imp*"
S: * LIST (\HasNoChildren \Important) "/" "Important Messages"
S: * LIST (\HasNoChildren) "/" "Imported Wine"
S: t1 OK Success
4. Security Considerations
The security considerations in [RFC6154], Section 7, apply equally to
this extension. In particular, "Conveying special-use information to
a client exposes a small bit of extra information that could be of
value to an attacker." Moreover, identifying "important" messages or
a place where important messages are kept could give an attacker a
strategic starting point. If the algorithm by which messages are
determined to be important is well known, still more information is
exposed -- perhaps, for example, there is an implication that the
senders of these messages are particularly significant to the mailbox
owner, and perhaps that is information that should not be made
public.
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As noted in RFC 6154, it is wise to protect the IMAP channel from
passive eavesdropping, and to defend against unauthorized discernment
of the identity of a user's "\Important" mailbox or of a user's
"$Important" messages.
5. IANA Considerations
This document contains 3 actions for IANA, specified in the sections
below:
1. Registration of the "$Important" keyword.
2. Creation of a new "IMAP Mailbox Name Attributes" registry.
3. Registration of initial entries in the "IMAP Mailbox Name
Attributes" registry.
5.1. Registration of the $Important keyword
IANA is asked to register the $Important keyword in the "IMAP
Keywords" registry, as follows, using the template in [RFC5788].
IMAP keyword name: $Important
Purpose (description): The "$Important" keyword is a signal that a
message is likely important to the user.
Private or Shared on a server: PRIVATE
Is it an advisory keyword or may it cause an automatic action: Adviso
ry (but see the reference for details).
When/by whom the keyword is set/cleared: The keyword can be set by
the user, or automatically by the system based on available
signals (such as who the message is from, who else the message
is addressed to, evaluation of the subject or content, or other
heuristics).
Related keywords: None (but see the reference for the related mailbox
name attribute).
Related IMAP capabilities: None.
Security considerations: See [[THIS RFC]], Section 4
Published specification: [[THIS RFC]]
Person & email address to contact for further information: IETF Appli
cations Area <apps-discuss@ietf.org>
Intended usage: COMMON
Owner/Change controller: IESG
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Note: None.
5.2. Creation of the IMAP Mailbox Name Attributes Registry
IANA is asked to create a new registry in the group "Internet Message
Access Protocol (IMAP)". The new registry will be called "IMAP
Mailbox Name Attributes", and will have two references: "RFC 3501,
Section 7.2.2", and "[[THIS RFC]], Section 5".
The registry entries will contain three fields:
1. Attribute Name
2. Description
3. Reference
IANA will keep this list in alphabetical order by Attribute Name,
which is registered without the initial backslash ("\").
The registration policy for the new registry will be listed as "IETF
Review or Expert Review" [RFC5226], and new registrations will be
accepted in one of two ways:
1. For registrations requested in an IETF consensus document, the
registration policy will be IETF Review, and the request will be
made in the IANA Considerations section of the document, giving
the requested values for each of the three fields.
2. For other registrations, the policy will be Expert Review policy
(see Section 5.2.1), and the request will be made by sending
email to IANA asking for a new IMAP Mailbox Name Attribute and
giving the requested values for each of the three fields.
5.2.1. Instructions to the Designated Expert
The expert reviewer, who will be designated by the IESG, is expected
to provide only a general review of the requested registration,
checking that the reference and description are adequate for
understanding the intent of the registered attribute. Efforts should
also be made to generalize the intent of an attribute so that
multiple implementations with the same requirements may reuse
existing attributes. Except for this check, this is intended to be
very close to a first come first served policy, and the expert should
not block serious registration requests with a reasonable reference.
The reference may be to any form of documentation, including a web
page, but consideration should be given to providing one that is
expected to be long-lived and stable.
5.3. Initial Entries for the IMAP Mailbox Name Attributes Registry
The registry will initially contain these entries:
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